Logging with skylines is an old, established technology. With the increased ecological pressures for selective logging, and the need to reach lumber on higher slopes, considerable scope exists to further exploit skyline logging, particularly if improvements are adopted over traditional techniques.
Generally, skylines are provided with an upper "tail-block" that is mounted on a post at the top of a slope to be logged extending downslope to a yarder or winch control system at its lower end. Such a tail-block arrangement is inherently fixed and limits the span of hill side that can be reached with a traditional skyline.
Proposals have been made for arrangements by which the upper terminal of a winching system may be shifted laterally to increase the terrain accessed by the winch. Examples include U.S. Pat. Nos. 95,611; 700,321; 1,489,448; 1,782,043; 3,270,895; 3,706,385; 3,499,544; 4,756,431; and Italian Patent 472,294. The references described, however, deal with tail-blocks which are in fixed positions until relocated, Such tail-blocks are not laterally adjustable in a controllable manner during logging.
U.S. Pat. No. 3,499,544 in particular shows a winch system in which an uphill winch tethered to a tree is supported vertically by pulleys that can transverse laterally, to a small degree, along a supporting cable 15. Such small motion may occur spontaneously in response to lateral loads, but they are not controllable laterally. The winch is said to be "shiftable" on the cable 13 (column 2, lines 53-56). As the winch in this patent is anchored to a tree or stump by a chain-stay 39 (column 3, line 25) such shifting must refer to the manual repositioning of the winch by disconnecting it from one portion of the cable 13. Thus, this arrangement lacks a tail-block positioning control system, for controllably positioning the winch laterally at specific locations along the transverse line.
U.S. Pat. Nos. 1,489,448 and 3,706,385 similarly describe a tail-block which is shiftable laterally to a series of separate positions. However, once fixed in each position, the tail-block in this disclosure is not controllable laterally during logging.
A further reference of interest is U.S. Pat. No. 3,333,713. This reference shows a traversing cable-supported hoist. In this reference two main lines extend in approximate parallel relationship up a slope. A lifting carriage in positioned between these two lines, supported by carriage-supporting cables extending to each line. These cable lengths are variable, allowing the position of the carriage laterally to be controlled. This system does not provide, however, for the shifting laterally of the two tail-blocks fixed at the upper ends of each of the main lines.
One object of this invention is, therefore, to provide a skyline for logging slopes wherein the position of the upper tail-block is shiftable laterally in a controllable manner to permit the tail-block to be located at selected positions transversely across a hillside during logging.
Balloons and kites have also been used for logging wherein their function is to lift the load of a log that is to be removed from a tract of lumber. United States patents that have issued in this category include: U.S. Pat. Nos. 3,221,897 3,270,895 3,326,392 3,270,895 3,346,127 3,359,919 3,369,673 3,448,864 3,706,385 3,807,577 3,865,251 4,055,319 4,640,474 5,080,302.
It has been recognized in such applications that control lines are required to position the balloon over a log to be lifted, and to transfer the log to the valley bottom for loading on to trucks. Patents U.S. Pat. No. 3,807,577 and U.S. Pat. No. 5,080,302 particularly address this issue.
A balloon-logging operation with control lines differs from a skyline in that the balloon control lines are not expected to carry any significant lifting loads. In a skyline,, however, the cables are expected to carry such loads. U.S. Pat. No. 3,706,385 particularly combines a balloon with a skyline in order to counteract the weight of the log-lifting carriage. While the use of a balloon-assist in a skyline system is therefore known, significant benefits are available by the combination of a balloon or balloons as part of the invention hereafter described.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification.